The present invention relates to an improved ceramic auxiliary combustion chamber. More particularly, the present invention relates to an auxiliary combustion chamber having a nozzle body mounted onto a cylinder head of an internal combustion engine such as a diesel engine or the like.
Engines which use an auxiliary combustion chamber to complete combustion in a relatively short time have been widely used in order to respond to the demand for miniaturization and high speed. In such engines, it is necessary to use a heat-resistant metal alloy as material for the body forming the nozzle of the chamber because it is subject to a high temperature in operation. Such heat-resistant metals are expensive and this results in increased cost thus causing a limited use.
In a auxiliary combustion chamber for a diesel engine or the like, in order to improve the combustion efficiency thereof by thermally insulating the same or to prevent parts thereof exposed to a high temperature from melting, ceramic auxiliary combustion chambers which are superior in adiabatic and heat-resistant properties have been studied and partly put to practical use.
Ceramics, however, have shortcomings in that they may be apt to be broken by thermal stress and they are brittle. To reduce thermal stress by reducing temperature gradients and to reduce assembling stress, a proposed device, as shown in FIG. 7, has been provided. In such a device, a ceramic nozzle body 3, having a nozzle 2 formed at its lower portion, is attached to a cylinder head 1 through a gasket 5 disposed on the upper portion of the nozzle body 3. A space 4 is maintained between the cylinder head 1 and the ceramic nozzle body 3 (Japanese Patent Unexamined Publication No. 59-200012).
In this proposed device, the nozzle body 3 is inserted after the gasket 5 has been mounted to the cylinder head 1, and therefore the side surface of the nozzle body 3 might come directly in contact with the cylinder head 1. When this occurs, thermal stress can arise by local heat removal from the nozzle body. Further, the gasket 5 and the ceramic nozzle body 3 are separately formed, and therefore the attaching of the gasket might be erroneously omitted. In the drawing, the reference numeral 6 designates a fuel injection nozzle, and the reference numeral 7 designates a glow plug.